Function pm#unary_function__unaryfunction (? -> ?)  function that requires a single argument; currently not specialized by the SUMO ternary relations since this seems useless (for now)
  type:  pm#function_type  term-forming relation that maps from a n-tuple of arguments to a range and that associates this n-tuple with at most one range element; note that the range is a set_or_class, and each element of the range is an instance of the set_or_class
  type:  pm#unary_function_type  class of functions requiring a single argument; if R is functional, then if R(x -> y) and P(x -> z) then y=z
  supertype:  pm#binary_relation (?,?)  in WebKB, most relation types are binary and some have a variable number of arguments (as in KIF), hence this type is currently only specialized by types that I do not want to see as direct subtypes of pm#relation
     supertype:  pm#relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
        supertype:  pm#relation__related_thing__relatedthing___related_with (*)  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type

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